1. Field of the Invention
The present invention relates generally to networking and communications technology.
2. Description of the Background Art
In the last few years, a technology has become adopted within the industry called Power over Ethernet (PoE) or Power over LAN. This technology allows local area network (LAN) devices to obtain power through the same data cable as they receive their network packets. Power is injected into the wiring pairs in a way that does not interfere with the signal quality of the LAN packets. This technology is gaining popularity as people see it useful for powering Internet Protocol (IP) telephones, Wireless Access Points (WAPs), and other remote devices that do not take a lot of power, and which are located in places where power distribution may be problematic.
The PoE technology enables the terminals, termed powered devices (PDs), to receive their operating power over the same Ethernet LAN connection that they use for data communication. It thus eliminates the need to connect each terminal to an AC power socket, and hence also eliminates the need to provide each terminal with its own AC/DC power converter.
The PoE technology also enables PDs to be recognized as such by a “signature” generated by the terminal. The LAN MAN Standards Committee of the IEEE Computer Society is developing specifications for Power over LAN systems, as described in IEEE Drafts P802.3af/D3.0 or later, entitled “Data Terminal Equipment (DTE) Power via Media Dependent Interface (MDI)” (IEEE Standards Department, Piscataway, N.J., 2001), which is also incorporated herein by reference. The specifications are referred to herein as standard 802.3af.
A PoE system may include an Ethernet switch and a power hub (Power Sourcing Equipment or PSE), which serves as the DC power source, along with a number of PD terminals, which communicate via the switch and draw power from the hub. The system is typically connected in a star topology, with each terminal linked by a cable to the switch and hub. The power hub in one chassis may be integrated with the switch in a second chassis, in a console containing both chassis, in what is known as an “end-span” configuration. Alternatively, the power hub chassis may be located between the switch chassis and the terminals, in a “mid-span” configuration. DC power is carried to the loads (i.e., the terminals) over twisted pairs provided by Category 5 cabling. The end-span configuration uses twisted-data-pairs that are also used for Ethernet communication; the mid-span configuration uses spare twisted-spare-pairs that are not used for Ethernet communication.